The present invention relates to welding electrodes and a process for forming same.
Resistance welding has long been used as a quick and effective method of joining metal members. The workpieces to be welded are placed in abutting relationship and a large current is caused to flow through the workpieces by a pair of opposed electrodes. The current causes the abutting surfaces of the workpieces to be heated sufficiently to effect the formation of a weld nugget. Typically, the electrodes apply significant pressure to the workpieces during welding. This facilitates the welding process by urging the material together and, also, reducing electrical resistance between each electrode tip and the adjacent workpiece material.
Since welding is accomplished by resistance heating of the material being welded, it will be appreciated that the electrodes will also be heated substantially. It is important to have an electrode of high electrical conductivity in order to minimize the power loss in the electrode and the resulting heating of the electrode.
Over time, the repeated heating and pressing operations involved in resistance welding cause breakdown, softening, mushrooming and other deformation of the electrodes. As this occurs, electrical current requirements increase with the enlarged welding tip face contacting the workpiece material until ultimately, redressing or replacement of the electrode is required. Accordingly, it is also important to have an electrode which is capable of withstanding significant distorting force at the elevated temperatures which result from the welding process so as to minimize the number of times it becomes necessary to redress or replace the electrode within a given period of time.
It is known in the art to form resistance welding electrodes by combining a copper electrode body with an anneal resistant high hardness insert. Typically, the insert performs much better than the copper material from which the electrode body was formed. However, the insert material is much more expensive than the copper used to form the electrode body.
The insert may be brazed onto the shank. The brazing step is disadvantageous as it adds an additional step to the electrode manufacturing process and, hence, increases the cost of the electrode. Furthermore, the brazing operation may anneal and soften the electrode body.
It is also known to force the insert into an electrode body via a press-fit operation. The steel being welded today is often galvanized, or coated with a zinc or other softer metal coating. As a result, the resistance welding electrodes tend to stick to the coated metal. An electrode tip joined to an electrode body via a press-fit operation may pull out of the shank during resistance welding of coated materials, thus requiring replacement of the electrode.
Accordingly, there is a need for an improved resistance welding electrode which can be manufactured via an efficient and more cost effective process and, yet, is capable of performing in an acceptable manner.